With IPHost Network Monitor you can run simple snmp requests against a Cisco device in your network.
cueMessageCount
cue Message Count
1.3.6.1.4.1.9.9.420.1.2.1.11
Total number of messages stored in all mailboxes.
Back to CISCO-UNITY-EXPRESS-MIB MIB page.
IPHost Network monitor allows you to monitor cueMessageCount on Cisco device via the SNMP protocol. Download IPHost Network Monitor (500 monitors for 30 days, 50 monitors free forever) to start monitoring Cisco firewalls right now.
